Re: [PATCH v2 1/1] efivarfs: fix statfs() on efivarfs

[Heinrich Schuchardt <heinrich.schuchardt@canonical.com>]

On 9/10/23 15:54, Ard Biesheuvel wrote:
> On Sun, 10 Sept 2023 at 15:08, Ard Biesheuvel <ardb@kernel.org> wrote:
>>
>> On Sun, 10 Sept 2023 at 06:53, Heinrich Schuchardt
>> <heinrich.schuchardt@canonical.com> wrote:
>>>
>>> Some firmware (notably U-Boot) provides GetVariable() and
>>> GetNextVariableName() but not QueryVariableInfo().
>>>
>>> With commit d86ff3333cb1 ("efivarfs: expose used and total size") the
>>> statfs syscall was broken for such firmware.
>>>
>>> If QueryVariableInfo() does not exist or returns an error, just report the
>>> file-system size as 0 as statfs_simple() previously did.
>>>
>>> Fixes: d86ff3333cb1 ("efivarfs: expose used and total size")
>>> Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
>>> ---
>>> v2:
>>>          initialize remaining_space to 0
>>
>> Thanks for the patch, and apologies for the oversight.
>>
>>> ---
>>>   fs/efivarfs/super.c | 20 ++++++++++++--------
>>>   1 file changed, 12 insertions(+), 8 deletions(-)
>>>
>>> diff --git a/fs/efivarfs/super.c b/fs/efivarfs/super.c
>>> index e028fafa04f3..3893aae6a9be 100644
>>> --- a/fs/efivarfs/super.c
>>> +++ b/fs/efivarfs/super.c
>>> @@ -29,14 +29,9 @@ static int efivarfs_statfs(struct dentry *dentry, struct kstatfs *buf)
>>>          const u32 attr = EFI_VARIABLE_NON_VOLATILE |
>>>                           EFI_VARIABLE_BOOTSERVICE_ACCESS |
>>>                           EFI_VARIABLE_RUNTIME_ACCESS;
>>> -       u64 storage_space, remaining_space, max_variable_size;
>>> +       u64 storage_space, remaining_space = 0, max_variable_size;
>>
>> Shouldn't storage_space be set to 0 too?
>>
>>>          efi_status_t status;
>>>
>>> -       status = efivar_query_variable_info(attr, &storage_space, &remaining_space,
>>> -                                           &max_variable_size);
>>> -       if (status != EFI_SUCCESS)
>>> -               return efi_status_to_err(status);
>>> -
>>>          /*
>>>           * This is not a normal filesystem, so no point in pretending it has a block
>>>           * size; we declare f_bsize to 1, so that we can then report the exact value
>>> @@ -44,10 +39,19 @@ static int efivarfs_statfs(struct dentry *dentry, struct kstatfs *buf)
>>>           */
>>>          buf->f_bsize    = 1;
>>>          buf->f_namelen  = NAME_MAX;
>>> -       buf->f_blocks   = storage_space;
>>> -       buf->f_bfree    = remaining_space;
>>>          buf->f_type     = dentry->d_sb->s_magic;
>>>
>>> +       /* Some UEFI firmware does not implement QueryVariable() */
>>> +       if (efi_rt_services_supported(EFI_RT_SUPPORTED_QUERY_VARIABLE_INFO)) {
>>> +               status = efivar_query_variable_info(attr, &storage_space,
>>> +                                                   &remaining_space,
>>> +                                                   &max_variable_size);
>>> +               if (status == EFI_SUCCESS) {
>>> +                       buf->f_blocks   = storage_space;
>>> +                       buf->f_bfree    = remaining_space;
>>> +               }
>>> +       }
>>> +
>>
>> I'd prefer not to ignore the error completely here. How about we do
>>
>> --- a/fs/efivarfs/super.c
>> +++ b/fs/efivarfs/super.c
>> @@ -32,10 +32,15 @@ static int efivarfs_statfs(struct dentry *dentry,
>> struct kstatfs *buf)
>>          u64 storage_space, remaining_space, max_variable_size;
>>          efi_status_t status;
>>
>> -       status = efivar_query_variable_info(attr, &storage_space,
>> &remaining_space,
>> -                                           &max_variable_size);
>> -       if (status != EFI_SUCCESS)
>> -               return efi_status_to_err(status);
>> +       /* Some UEFI firmware does not implement QueryVariableInfo() */
>> +       storage_space = remaining_space = 0;
>> +       if (efi_rt_services_supported(EFI_RT_SUPPORTED_QUERY_VARIABLE_INFO)) {
>> +               status = efivar_query_variable_info(attr, &storage_space,
>> +                                                   &remaining_space,
>> +                                                   &max_variable_size);
>> +               if (status != EFI_SUCCESS && status != EFI_UNSUPPORTED)
>> +                       return efi_status_to_err(status);
>> +       }
>>
>>          /*
>>           * This is not a normal filesystem, so no point in pretending
>> it has a block
>>
>> (no need to resend if you agree)

Hello Ard,

thanks for reviewing.

Raising an error in such a rare circumstance would be ok for me.

> 
> Actually, perhaps it would be better to simply fall back to the old
> logic if QueryVariableInfo is not provided:
> 
> diff --git a/fs/efivarfs/super.c b/fs/efivarfs/super.c
> index e028fafa04f3..50b05f1fa974 100644
> --- a/fs/efivarfs/super.c
> +++ b/fs/efivarfs/super.c
> @@ -30,10 +30,15 @@ static int efivarfs_statfs(struct dentry *dentry,
> struct kstatfs *buf)
>                           EFI_VARIABLE_BOOTSERVICE_ACCESS |
>                           EFI_VARIABLE_RUNTIME_ACCESS;
>          u64 storage_space, remaining_space, max_variable_size;
> -       efi_status_t status;
> +       efi_status_t status = EFI_UNSUPPORTED;
> +
> +       if (efi_rt_services_supported(EFI_RT_SUPPORTED_QUERY_VARIABLE_INFO))
> +               status = efivar_query_variable_info(attr, &storage_space,
> +                                                   &remaining_space,
> +                                                   &max_variable_size);
> +       if (status == EFI_UNSUPPORTED)
> +               return simple_statfs(dentry, buf);

I would not know why the block size (buf->f_bsize) should depend on the 
availability of QueryVariableInfo() (1 vs PAGE_SIZE).

Hence I would prefer your suggestion to just add the error handling 
suggested in your previous mail.

Best regards

Heinrich

> 
> -       status = efivar_query_variable_info(attr, &storage_space,
> &remaining_space,
> -                                           &max_variable_size);
>          if (status != EFI_SUCCESS)
>                  return efi_status_to_err(status);